Panadapter
| Panadapter | |
|---|---|
| Short for | Panoramic adapter |
| What it shows | A live picture of signals across a range of frequencies |
| Display types | Spectrum (strength against frequency) and waterfall (frequency against time, with strength as color) |
| Also called | Spectrum scope, bandscope |
| Hardware | |
| Built in | Most current transceivers with SDR circuitry |
| External | An SDR receiver connected to a radio's IF output or receive-antenna port |
| Typical software | HDSDR, SDR Console, SDR++ |
| Key settings | Span, reference level, averaging, waterfall speed |
A panadapter is a display that shows the signals across a whole slice of a band at once, rather than just the one frequency a receiver is tuned to. The name is short for panoramic adapter, from the days when it was a separate unit added to a communications receiver. Today a panadapter is built into most new HF transceivers, usually called a spectrum scope, and it is the most visible feature of software-defined radio. For newcomers it turns an apparently empty band into a map of where the activity is.
Spectrum and waterfall
Most panadapters offer two views, often stacked one above the other.
- The spectrum display plots frequency across the screen and signal strength up the screen. Each signal is a peak, and the background noise forms a ragged baseline sometimes called the grass.
- The waterfall draws each moment as one line of color, with stronger signals brighter, and scrolls the lines downward to build a running history. Signals become vertical trails, and their shapes reveal the mode.
On a waterfall, CW appears as a thin dotted line, SSB voice as an irregular band roughly 2.5 kHz wide, RTTY as two parallel traces, FT8 as rows of short blocks in a narrow segment, and an unmodulated carrier as a solid line. Because the eye adds up a signal's trail over time, the waterfall often shows weak signals that are invisible on the spectrum display.
How it works
Older bandscopes worked like a swept spectrum analyzer, stepping a receiver repeatedly across the range and plotting what it found, which made them slow and coarse. A modern panadapter digitizes a band of frequencies and uses a fast Fourier transform (FFT), a calculation that splits a block of samples into its frequency components, to compute the whole span at once. A direct-sampling radio can display an entire band, or more, in real time.
Common settings include:
- Span, the width shown, from a few kilohertz to a whole band.
- Center or fixed mode. In center mode the display stays centered on the tuned frequency and scrolls as the dial turns; in fixed mode the band edges stay put and a marker moves.
- Reference level and averaging, which set the brightness of the noise floor and smooth the display.
- Waterfall speed, a trade between seeing quick changes and keeping a longer history.
Using a panadapter
- Finding activity. Stations are visible at a glance, and on most radios a click or touch on a signal tunes to it. A glance across the screen also shows whether a band is open at all.
- Finding a clear frequency before calling CQ.
- Working split. In a DX pileup, the panadapter shows where the callers are spread and often where the station just worked was calling, which helps in split operation.
- Contesting. Contest operators search for unworked stations far faster with a display than by tuning.
- Spotting problems. Wide, splattering signals and key clicks stand out, and a row of evenly spaced signals across the band is a classic sign of a noisy switching power supply, a useful clue when hunting interference.
A panadapter shows what the receiver sees, including any false signals created by overload, so a very strong local station may appear to have spurs that are really inside the receiver.
External panadapters with SDRs
A radio without a built-in display can gain one from an inexpensive SDR receiver and a computer. There are two common ways to connect it:
- IF tap. Some radios have an IF output jack, and others can have a buffered tap fitted inside. The SDR then views the radio's IF, so the display follows the radio's tuning automatically.
- Antenna side. The SDR is fed from the radio's receive-antenna output, or through a transmit-receive switch that disconnects it whenever the radio transmits.
Software such as HDSDR or SDR Console links the SDR and the transceiver through the radio's computer control (CAT) port, so tuning either one moves the other, and clicking a signal on the waterfall tunes the radio. A WebSDR offers a similar view of a remote receiver through a web browser.